Solvent extraction method



April 7, 1970 E. F. NELSON SOLVENT EXTRACTION METHOD Edwin F. NelsonKZ/Mm, y. TTR/V-YS United States Patent O 3,505,202 SOLVENT EXTRACTIONMETHOD Edwin F. Nelson, Arlington Heights, Ill., assignor to UniversalOil Products Company, Des Plaines, Ill., a corporation of Delaware Filed.lune 26, 1967, Ser. No. 648,871

Int. Cl. Cg l/00 U.S. Cl. 208-8 10 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF THE INVENTION This invention relates to a solventextraction method. It also relates to a method for liquefying coal usinga selective solvent.

It has long been known that hydrocarbon gases, liquids, and pitch, and,the chemicals derived from or allied to these hydrocarbons, may beobtained in some form from coal which is mined from the earth. Usually,the prior art has employed destructive distillation or othergasification processes for the conversion of coal into these morevaluable ande useful products. Recently, the prior art has used highpressure hydrogenation of coal to make this conversion. Othersatisfactory methods for the obtaining of useful fuels and chemicalsfrom coal have involved the solvent extraction technique whereby thecoal is contacted with a selective solvent which acts as a hydrogendonor for supplying suicient hydrogen to the coal to aid in convertingit into a liquid phase. Following the solvent extraction step, the priorart schemes have utilized various recovery procedures, such ashydrogenation of the liquid coal extract for increasing its value andutility together with retorting or coking of the residual materialsobtained from the solvent extraction step to still further convert thesecoal-derived products into more valuable products.

Since it is clear to those skilled in the art that the vast mineralreserves of Ibituminous coal represent an extremely important supply ofenergy, it would be desirable to improve upon the prior art processes inorder to reduce the cost of obtaining typically petroleum-type productsfrom coal.

SUMMARY OF THE INVENTION Therefore, it is an object of this invention toprovide a method for the liquefaction of coal whereby valuablehydrocarbon products may be obtained therefrom.

It is a specific object of this invention to provide an improved methodfor subjecting pulverized coal to solvent extraction using, for example,Tetralin as the solvent.

Therefore, in accordance with the practice of one embodiment of thisinvention, there is provided a method for the liquefaction of coal whichcomprises admixing lump bituminous coal with solvent and then subjectingthe admixture to coal pulverization conditions.

It is another embodiment of this invention to utilize the methodhereinabove wherein the solvent comprises an at least partiallyhydrogenated polycyclic hydrocarbons.

Still another embodiment of this invention includes the method for theliquefaction of coal which comprises the steps of: (a) admixing lumpbituminous coal with a solvent comprising an at least partiallyhydrogenated polycyclic hydrocarbon; (b) subjecting said admixture toICC coal pulverization conditions including a relatively high.temperature sufficient to at least partially dissolve coal into thesolvent; (c) passing the pulverized coal-solvent product into adigestion zone maintained under conditions sutlicient to substantiallydissolve the pulverized coal; and (d) recovering liquid coal extractfrom the digestion zone in high concentration.

Thus, it is to be noted from the description of the in- ,ventionpresented thus far that the benefits to be derived from the practicethereof are predicated on the theory that having the presence of thesolvent during the pulverization step of the coal results in asubstantial increase in the etliciency of the operation and, as will bemore fully developed hereinbelow, results in a decreased use of solventfor obtaining the same amount of liquid coal extract.

It is believed that the benets obtained from the practice of thisinvention are predicated on the hypothesis that at the point of shearfor the crushing and grinding of the coal, the shear site is extremelyreactive and hydrogen, therefore, can be transferred into that site moreearily than if the coal is pulverized prior to contact with the solvent.In addition, the small particles of coal which are sheared away from alarge lump immediately expose not only the highly reactive shear site tothe solvent, but also exposes an extremely large surface area to thesolvent, thereby enabling these small particles of coal to almostimmediately dissolve in the solvent and become a part 0f the liquid coalextract. While not desiring to be limited by this theory, the practiceof this invention is at least explained to those skilled in the art sothat future work may be used along these lines to even further improveupon the inventive concepts contained herein.

Additionally, there has been some discussion in the prior art that thepresence of oxygen or oxygen compounds on the surface of the coal makesit difficult for the coal to react properly with the suitable solventsfor the conversion thereof into liquid coal extract. Therefore, by

pulverizing or crushing the coal in the presence of a liquid solvent,oxygen compounds or the presence of oxygen have been excluded from thehighly reactive shear sites along the coal thereby enabling the transferof the' hydrogen from the solvent to the coal to become of significantlyincreased eiciency.

The coal preferred for use in the practice of the present inventivemethod is of the bituminous type, such as Pittsburgh Seam Coal. Morepreferably, however, the bituminous coal is a high volatile content coalhaving a volatile content greater than about 20% by weight of the m.a.f.coal (moisture and ash-free coal).

The extraction of coal by means of solvent has been proposed bydefinition as partial conversion of the coal since not only is the coalreacted with the hydrogen which is transferred from the solvent butthere is also a solution phenomenon which actually dissolves the coal,which has accepted the hydrogen into the solvent. Therefore, as usedherein, the term liquid coal extract and liquefied coal fraction isintended to include the liquid product which is obtained from thesolvent extraction of the coal with the selective solvent, and will begenerally described on the basis of being solvent-free, even though aportion of extract comprises hydrocarbons suitable for use as thesolvent. The practice of the present invention is performed underconditions which increase the kinetics of the reaction while maintainingthe components therein in primarily liquid phase; although, in somecases, it may be desirable to practice this invention in the presence ofa vaporized solvent by using a vaporous pulverization technique.

Suitable solvents for use in the practice of this invention in theextraction step are those which are of the hydrogen donor type and areat least partially hydrogenated and include naphthenic hydrocarbons.Preferably, the solvent is one which is in liquid phase at therecommended temperature and pressure for the extraction andpulverization step. Mixtures of the hydrocarbons are generally employedand, preferably, are derived from intermediate or iinal productsobtained from subsequent processing following the practice of thisinvention. Typically, these solvent hydrocarbons or mixture ofhydrocarbons boil between about 260 C. and 425 C. Examples of suitablesolvents are tetrahydronaphthalene (Tetralin), decahydronaphthalene(Decalin), biphenyl, methylnaphthalene, d-imethylnaphthalene, etc. Othertypes of solvents which may be added to the preferred solvents of thisinvention for special reasons include phenolic compounds such asphenols, cresols, and xylenols. It is also to be recognized that in somecases it may be desirable during a subsequent separation step prior tothe removal of the solvent from the liquid coal extract to add ananti-solvent, such as a saturated paraffinic hydrocarbon like hexane, toaid in the precipitation of tarry and solid residues from the coalextract of the invention.

Apparatus for use in pulverizing the lump or coarse coal feed to thepresent invention may be of any type known to those skilled in the art.Conventional ball mills or rod mills may be used with satisfactoryresults. The only requirement for the apparatus in the practice of thisinvention is that the apparatus must be able to pulverize lump or coarsecoal in the presence of significant quantities of liquid solvent Withoutdifiiculty. Those skilled in the are are familiar with the kinds ofapparatus for processing wet solids and the crushing and grindingthereof such that no detailed discussion of the apparatus need bepresented herein. The primary requirement for crushing and grinding ofthe lump coal in the presence of the selective solvent is that coarsecoal usually having an average particle diameter in excess of 0.08 inchand, typically, between about 0.25 and 2.0 inches must be processedthereto and reduced in size to an average particle diameter which wouldbe of at least a --8 Tyler screen size, and preferably, would be reducedto an average particle size for -14 Tyler screen size. As used herein,the term Tyler screen refers in all instances to the commercial TylerStandard Screens. The correlation between Tyler screen mesh and averageparticle diameter is as follows:

Average diameter of Tyler screen mesh: particles D,wg in.

The conditions during the pulverization step may be varied widelyaccording to the desires of those skilled in the art and practicing thisinvention. The temperature` of course, may be varied over a relativelybroad range from essentially atmospheric temperature to a relativelyhigh temperature. It is distinctly preferred in the practice of thisinvention that the temperature of the coal and the solvent be maintainedat a relatively high temperature, say, from 300 C. to 500 C. Thepressure, in similar manner, may be varied over an extremely wide rangefrom atmospheric pressure to, say, 10,000 p.s.i.g. with a preferredpressure being about 100 p.s.i.g. or typically about 70 p.s.i.g.

The operation of the pulverizing equipment is preferably performed sothat the oversized material; that is, greater in size than the minus 8Tyler screen size, be separated and returned to the apparatus forfurther pulverizing. The utilization of the closed circuit technique iswell known to those skilled in the art, and is preferred in the practiceof this invention. Unless otherwise stated, closed circuit operation ofthe pulverization equipment will be deemed inherent in the practice ofthis invention.

The amount of solvent which is used during the pulverization stepgenerally will range from 0.2 to l0 pounds of solvent per pound of coal.Satisfactory results may be obtained in the practice of this inventionin utilizing approximately equal amounts of solvent to coal on a weightbasis. The conditions during the pulverization step should be chosensuch that the coarse coal is reduced in size to at least a -8 Tyleryscreen size and the solvent has a chance to react and dissolve the coalto an extent such that the coal particles are at least partiallydissolved in the solvent.

It is an essential feature of this invention that the pulverization stepbe not only a mechanism for reducing the 'size of the coal, but also beused to at least partially dissolve the coal in the solvent. In otherwords, as will be more fully evident from the discussions presentedhereinafter, the present invention is in some respects a two-stagesolvent extraction step. In the practice of this invention theconditions chosen in the pulverization step will be such that from 10%to 40% by weight of the m.a.f. coal is dissolved in the solvent with atleast an additional 50% by weight being dissolved during the subsequentdigestion zone, more fully discussed hereinafter.

Following the size reduction step wherein at least part of the coal hasbeen dissolved in the solvent and the oversized solid materials havebeen separated, the eiuent product comprising solvent, having dissolvedtherein liquid coal extract, and undissolved solid coal is passed into adigestion zone which is a reaction zone for the substantial conversionof the coal into liquid coal extract. The operating conditions for thedigestion zone include a temperature from 300 C. to 500 C., a pressurefrom atmospheric to 10,000 psig., a solvent to coal weight ratio from0.2 to 10, and a residence time from 30 second to 5 hours, suflicient todissolve coal such that a total in excess of 50% by weight of maf. coalhas been liquefied. It is to be noted that the temperature and pressureconditions during the digestion zone may be the same, may be higher, maybe lower, or may be any different conditions during the digestion zonemay be the same, may be higher, may be lower, or may be any differentconguration desired by those skilled in the art over those conditionsmaintained in the pulverization zone. It has been found satisfactory inthe practice of this invention that the temperature and pressure in thedigestion zone be maintained essentially at the same level as thetemperature and pressure maintained in the pulverization zone.

Since the purpose of the digestion zone is to substantially complete theconversion of the coal into a liquid coal extract, it may be desirableto add additional solvent to the zone, add a hydrogen-containing gas tothe zone, and/or utilize a catalyst in the digestion zone. The catalystused may be conventional, may be homogenous or heterogenous and may beintroduced in the pulverization zone and/or digestion zone in admixturewith the liquid solvent or with the solid coal. Those skilled in the artfrom a knowledge of the characteristics of the coal, the solvent, andthe properties desired for the endproduct will know whether or not itmay be desirable to use any or all of these additional features in thedigestion zone. Conventional hydrogenation catalyst may be desirable;such as palladium on an alumina support, or a cobalt-molybdate catalystor any other hydrogenation catalyst known to those skilled in the artand applicable to the solvent-coal system environment maintained in thedigestion zone including the use of a slurrycatalyst system.

After separation of the solvent and undissolved coal residue (andcatalyst, if any from the total efluent of the digestion zone, theliquid coal extract is further processed by means known to those skilledin the art such as conventional hydrogenation treatment to convert theliquid coal extract into more valuable products, such as fuel, e.g.gasoline boiling range products, and/or chemicals, such as aromatichydrocarbons, the utility of which is well known.

The invention may be more fully understood with reference to theappended drawing which is a schematic representation of apparatus forpracticing one embodiment of the present invention.

DESCRIPTION OF THE DRAWING Referring now to the drawing, coarse coalhaving an average particle diameter, generally, in excess of 0.08 inchis introduced into the system via line 10. A suitable selective solventfor the coal is introduced into admixture with the coarse coal from line11, by means more fully hereinafter discussed; the oversized solidmaterial from the pulverizing zone is also preferably returned to thepulverizing zone via line 12. The entire admixture of coarse coal andsolvent is passed via line 13 into mill 14 which conventionally may beof the ball mill type.

Suitable pulverization conditions including a temperature from 300 C. to500 C. is maintained in mill 14 such that the coarse coal is reduced toan average particle diameter between 0.08 and 0.04 inch and at least aportion of the coal, say from to 40% by weight is dissolved into thesolvent.

The eflluent from mill 14 containing solvent having dissolved thereinthe liquid coal extract, undissolved coal of proper small particle size,and undissolved coal of oversize is passed via line 15 into separator 16which may be of the cyclone type. Conditions are maintained in separator16 whereby the oversize coal particles, preferably in admixture with atleast a portion of the liquid material, is removed via line 12 andreturned to mill 14 in a manner previously discussed.

The solvent having dissolved therein the liquid coal extract plusundissolved pulverized coal is passed via line 17 into digestion zone 19which may be of a jacketed, stirred-type vessel. Added solvent, if any,may be introduced to the system via line 18 in an amount sufficient tomaintain the solvent to coal ratios at the desired levels both indigester 19 and mill 14. Control of the solvent dosage to mill 14 willbe more fully discussed hereinafter.

The entire eluent from digestion zone 19 is passed via line 20 intofirst separation zone 21 wherein conditions are maintained suicient tobegin settling and agglomerating the coal residues and solid materials.As previously mentioned, if desired, by means not shown, an anti-solventsuch as hexane may be added to zone 21 in an effort to further aid inremoving tars and solid materials from the desired solvent and liquidcoal extract. An eluent stream from zone 21 is removed via line 22 andpassed into filtration zone 23 which is operated in such a manner thatthe solid coal residue may be withdrawn via line 24 and thesolvent-liquid coal extract stream may be withdrawn via line 25.

The mother liquor from the filter 23 is passed via line 25 into secondseparator 26 which may be of a conventional distillation column type.Suitable conditions are maintained therein such that a distillatefraction comprising lean solvent may be withdrawn via line 27 andpreferably is returned to admixture with the incoming coarse coal feedfrom line 10, as previously mentioned. The remaining liquid coal extractis removed from separator 26 via line 28 for further processing inaccordance with practices known to those skilled in the art includinghydrogenation techniques for upgrading the liquid coal extract to thedesired valuable product of motor fuel and/or chemicals. Means (notshown) for removing the Illustrative of a prior art scheme, a PittsburgSeam Coal lwas rst pulverized to an average particle diameter of -14Tyler mesh size. The pulverized coal was treated in a solvent extractionzone with Tetralin solvent under the following conditions:

Temperature-'380 C. Pressurep.s.i.g. Solvent/ coal-1.0 Residencetime-1.0 hour The yield from this extraction treatment was 57.8% byweight of liquid coal extract (solvent-free) based on the originalm.a.f. coal. Thus, based on a use of pounds of solvent per 100 pounds ofpulverized coal, the prior art obtained about 58 pounds of liquid coalextract.

Example 2 Illustrative of the instant inventive method, a Pittsburg eamCoal, coarse size, was admixed with an equal weight of Tetralin solventand the mixture subjected to crushing and grinding in a ball mill. Afterseparation and recycle to the mill of the oversize particles, the entireproduct from the ball mill including solid coal particles of -14 Tylermesh average particle diameter, liquid extract and solvent, was passedinto a digester. The following conditions Were maintained for eachdesignated step:

Ball mill Digester Temperature, C 380 38 0 Pressure, p.s.i.g.. 70Solvent/coal ratio.. 1. 0 Residence time, hours 1. 0 Liquid coalextract,l percent-.. 2 50 1 Solvent-free basis. 2 Additional.

It is noted that the inventive method accomplishes a significantincrease in liquid coal extract under substantially the same conditionsincluding the same amount of solvent as used in Example 1. It is furtherbelieved that the liquid coal extract obtained from the inventiveprocess contained no more benzene-insoluble material proportionatelythan the extract obtained from Example 1.

PREFERRED EMBODIMENT A preferred embodiment of the present inventionincludes a method for the liquefaction of coal which comprises the stepsof: (a) admixing coarse size bituminous coal with a solvent comprisingat least partially hydrogenated polycyclic hydrocarbons boiling betweenabout 260 C. and 425 C.; (b) introducing the solvent-coarse coaladmixture into a pulverization zone under conditions including atemperature from 300 1C. to 50.0 C., pressure from atmospheric to 10,000p.s.i.g., solvent to coal weight ratio from 0.2 to 10 sufficient toreduce said coarse coal to at least a -8 Tyler screen size and to atleast partially dissolve coal into said solvent; (c) passing thepulverized coal-solvent product including dissolved coal from thepulverization zone into a digestion zone maintained under conditionsincluding a temperature from 300 C. to 500 C., pressure from atmosphericto 10,000 p.s.i.g., solvent to coal weight ratio from 0.2 to 10, and aresidence time from 30 seconds to 5 hours suicient to dissolve coal suchthat a total in excess of 50% by -weight of rn.a.f. coal is liqueed; (d)introducing the total effluent from the digestion zone into a separationzone under conditions suicient to produce a solvent fraction, a liqueedcoal fraction, and a solids fraction comprising undissolved coal; and,(e) recovering said liqueed coal fraction in high concentration.

Another preferred embodiment of the present invention includes a methodfor liquefying coal which involves size reduction of the feed coal andsolvent extraction to dissolve pulverized coal particles, theimprovement which comprises pulverizing coarse size feed coal in thepresence of said solvent to an average particle diameter smallel than0.08 inch.

The invention claimed:

1. Method for the liquefaction of coal which comprises the steps of (a)admixing lump bituminous coal prior to pulverization thereof with asolvent comprising an at least partially hydrogenated polycyclichydrocarbon;

(b) subjecting said admixture to coal pulverization conditions includinga relatively high temperature suflcient to at least partially dissolvecoal into said solvent during shearing of the coal;

(c) passing the pulverized coal-solvent product into a digestion zonemaintained under conditions suflcient to substantially dissolve thepulverized coal; and

(d) recovering liquid coal extract from the digestion zone in highconcentration.

2. Method according to claim 1 wherein said solvent comprisestetrahydronaphthalene.

3. Method according to claim 1 wherein said pulverization conditionsinclude a temperature from 300 C. to 500 C.

4. Method according to claim 1 wherein said digestion conditions includethe presence of a catalyst.

5. Method for the liquefaction of coal which comprises the steps of:

(a) admixing coarse size bituminous coal prior to pulverization thereofwith a solvent comprising at least partially hydrogenated polycyclichydrocarbons boiling between about 260 C. and 425 C.;

(b) introducing the solvent-coarse coal admixture into a pulverizationzone under conditions including a temperature from 300 C. to 500 C.,pressure from atmospheric to 10,000 p.s.i.g., solvent to coal weightratio from 0.2 to l sufficient to reduce said coarse coal to at least a-8 Tyler screen size and to at least partially dissolve coal into saidsolvent during shearing of said coal;

(c) passing the pulverized coal-solvent product including dissolved coalfrom the pulverization Zone into a digestion zone maintained underconditions including a temperature from 300 C. to 500 C., pressure fromatmospheric to 10,000 p.s.i.g., solvent to coal weight ratio from 0.2 to10, and a residence time from 30 seconds to 5 hours suicient to dissolvecoal such that a total in excess of by weight of maf. coal is liquefied;

(d) introducing the total eiuent from the digestion zone into aseparation zone under conditions sufricient to produce a solventfraction, a liquefied coal fraction, and a solids fraction comprisingundissolved coal; and

(e) recovering said liqueed coal fraction in high concentration.

6. Method according to claim 5 wherein said solvent fraction of step (d)is returned to step (a) for admixture with coarse size coal asspecified.

7. Method according to claim S wherein said solvent comprises Tetralin.

8. Method according to claim 5 wherein said coarse coal is reduced instep (b) to an average particle diameter between 0.08 to 0.04 inch.

9. Method according to claim 8 wherein from 10% to 40% by Weight of coalis dissolved in the pulverization zone and at least an additional 50% byweight is dissolved in the digestion zone.

i0. Method according to claim 9 wherein at least a portion of thesolvent is selected from the group consisting of tetrahydronapthalene,decahydronaphthalene, biphenyl, methylnaphthalene, anddimethylnaphthalene.

References Cited UNITED STATES PATENTS 1,672,231 6/ 1928 Ryan 208-111,940,648 12/ 1933 Russell 208-8 1,934,023 11/1933 Wright 208-102,174,184 9/1939 Bywater 208-8 3,018,242 l/1962 Gorin 208-10 2,738,3113/1956 Frese et al. 208-8 3,075,912 1/ 1963 Eastman et al 208-83,018,241 1/1962 Gorin 208-8 DELBERT E. GANTZ, Primary Examiner r V.OKEEFE, Assistant Examiner U.S. Cl. X.R. 208-10

